The aspect ratio defines the ratio of the width of the picture to its height. The aspect ratio of a commercial movie theater's screen is at least 5:3, and the conventional United States television picture, as specified by the National Television Standards Committee (NTSC) is 4:3. In addition, a commercial movie theater's picture is of higher resolution than that of conventional United States television. An approach for providing high-definition television with an extended aspect ratio is described in the U.S. patent application of J. L. LoCicero, et al., Case LoCicero-Pazarci-Rzeszewski 2-2-6, entitled, "Compatible High-Definition Television With Extended Aspect Ratio", filed June 29, 1984, Ser. No. 626,453. This application discloses a television system having a fully compatible high-definition signal with extended aspect ratio information receivable at conventional resolution by conventional TV receivers without auxiliary apparatus with one TV channel carrying the conventional TV signal, while high-frequency luminance and chrominance information plus extended aspect ratio information are provided in a second TV channel. The picture displayed by this TV system consists of a high-resolution center segment and two low-resolution edge segments. Since the human eye tends to focus on the center of the TV screen, the perception is that the viewer is observing a high-resolution extended aspect ratio picture and, in general, does not detect the low-resolution in the two edge segments. The LoCicero, et al., application discloses a TV receiver which, after reception of the transmitted signal, decodes high- and low-resolution luminance and chrominance information into individual signals and then recombines the low- and high-resolution luminance signals and the low- and high-resolution chrominance signals by gating and summing these signals at the appropriate times.
Whereas, the straight-forward approach utilized by the LoCicero, et al., application gives adequate performance where the transmitter and receiver filters are well known and the transmission media is stable, the filters used in the transmitter and receiver as well as the transmission media can cause distortion to appear at the point on the screen where the low-resolution and high-resolution segments come together. One of the reasons for the distortion is the use of filters in both the receiver and transmitter with flat pass-band responses and high stop-band attenuation characteristics. Such filters generally have oscillatory transient responses with overshoots and undershoots. The other processing blocks within the transmitter and receiver also have transient responses. By the time the transmitted signal is received at the decoder portion of the TV receiver, since both the edge and center information have been passed through a number of processing blocks with different transient responses, the abrupt change at the joining point between the low-resolution edge portion of the picture and the high-resolution center portion of the picture has been corrupted by the transient responses of the different processing units. If this corruption is significant, then the mere gating and summing of the edge and center luminance and chrominance information will leave visible and annoying artifacts appearing at the joint.
Therefore, there exists a need for apparatus that can eliminate or compensate for the transients due to the processing units in both the transmitter and the receiver of a television signal such that the low-resolution edge and high-resolution center segments of a picture in a high-definition television system with extended aspect ratio can be displayed without annoying artifacts in the proximity of the joint between the different segments.